As shown in FIG. 9, optical drop cables 10 are typically used to connect an outdoor optical cable feeder 31 stretched between power poles to individual houses 33 through an optical closure 34. As shown in FIGS. 1 to 4, optical drop cables 10 typically comprise optical fiber cores 11 and tension (resistant) members 12 provided on both sides of the cores 11 which are covered by resin together with a support wire (suspension wire) 13 (see JP Patent Publications 2002-090593A and 2002-328276A).
As shown in FIG. 9, because such optical cables 10 are used outdoors, cicadas (and other insects) fly to them. Some cicadas deposit eggs directly in bark by sticking their ovipositors into the bark. Others form bite marks in the bark and deposit eggs in the bark through the bite marks.
Among such cicadas, black cicadas have especially strong ovipositors. Thus, if eggs are deposited by black cicadas in the outer sheath 15 of an optical drop cable 10, which is made of resin, their ovipositors frequently damage or entirely break the optical fiber cores (element wires) 11 when the ovipositors are stuck into the outer sheath 15.
In order to prevent the ovipositors of black cicadas from getting stuck in optical drop cables, JP Patent Publications 2002-090593A and 2002-328276A propose to improve notches 14, through which ovipositors are likely to get stuck in the cable.
JP Patent Publication 2006-65288A proposes to provide an outer sheath 15 having a circular outer sectional shape so that black cicadas cannot easily land on the cable.
In particular, in JP Patent Publications 2002-090593A and 2002-328276A, the apex of each notch 14 is oriented so as not to face the optical fiber cores 11, thereby preventing ovipositors from getting stuck into the cable toward their optical fiber cores 11.
But every cicada does not necessarily stick its ovipositor in a direction away from the optical fiber cores 11 (and toward the apex of the notch 14). Some cicadas may stick their ovipositors toward the optical fiber cores 1. In such a case, the optical fiber cores 11 may be damaged or broken.
The arrangement of JP Patent Publication 2006-65288A is effective to a certain extent. But it was discovered that ovipositors were stuck in the outer sheaths 15 of some of such cables. Thus, this arrangement cannot sufficiently prevent ovipositors from getting stuck in optical drop cables.